1. Field of the Invention
The present invention relates to a charged particle beam apparatus which processes an object with a charged particle beam, a drawing apparatus, and a method of manufacturing an article.
2. Description of the Related Art
An apparatus which processes an object with a charged particle beam, such as an electron beam drawing apparatus (electron beam exposure apparatus) or a scanning electron microscope, has a function of measuring and adjusting the intensity of the charged particle beam. An electron beam drawing apparatus will be taken as an example. Conventionally, to measure the intensity of an electron beam, a detector such as a Faraday cup, or a photodiode having a function of multiplying electrons is used. As the amount of charges gets smaller, the S/N ratio lowers in the Faraday cup, so the charge output is measured using a detector such as a photodiode, as disclosed in Japanese Patent Laid-Open No. 2005-56923. The electron beam drawing apparatus monitors and adjusts the intensity of an electron beam to control, for example, the line width of a pattern to be drawn.
The width of a pattern to be drawn reduces each year. With a reduction in pattern width, the size of an electron beam also reduces. To draw, for example, a pattern having a line width of 22 nm, the beam must have a size equal to or half that of this line width. Also, to perform drawing at high speed, an electron beam with a high intensity is emitted in a short time. When the line width of a pattern is not minute, the beam size used in the electron beam drawing apparatus can be increased. However, in a drawing apparatus which uses a plurality of electron beams, no lens for increasing the beam size can be interposed between an objective lens and a stage which holds a substrate. Therefore, the energy density of an electron beam increases, so a 1-nm2 region is irradiated with an electron beam having an accelerating voltage of several tens of kiloelectronvolts.
When an electron beam having a given energy is incident on a detector (for example, a semiconductor detector formed by, for example, Si or Ge) having a function of multiplying electrons, charges (electron-hole pairs) are generated in correspondence with the number of incident electrons. The detector can output a voltage signal by converting the generated charge into a voltage using an amplifier. The detector also can extract a current resulting from the generated charge as a voltage signal via an amplifier which converts a current into a voltage.
When the surface of a detector which monitors the intensity of an electron beam, and an internal thin film are irradiated with an electron beam having a high charge density for a long time, the detector suffers damage. When the detector suffers damage, the efficiency of generating charges by the detector decreases. The decrease in efficiency of charge generation leads to a reduction in signal output, that is, degradation in sensitivity of the detector when the intensity of an electron beam is measured. When an electron beam is incident only on a specific region on the detection surface of the detector, the sensitivity in the specific region on the detection surface degrades. When the sensitivity of the detection surface varies, the magnitude of the output signal varies depending on the incident position of an electron beam on the detector, so the intensity of the electron beam cannot be measured with high accuracy.
FIG. 4 shows the procedure of measuring the intensity of an electron beam in the conventional technique. In step S1, the detector moves to a predetermined position at which the intensity of an electron beam is measured. In step S2, the intensity of an electron beam is measured. In step S3, data corresponding to the intensity of the electron beam obtained by measurement is stored. If it is determined in step S4 that an electron beam to be measured remains, steps S1, S2, and S3 are repeated; otherwise, the sequence of measurement ends. In the conventional technique, the incident position of an electron beam on the detector is not changed. Therefore, the incident region of an electron beam is the same region which has a certain size and depends on the positioning accuracy of a stage on which the detector is set, and the control accuracy of the incident position of the electron beam. That is, in the conventional technique, an electron beam is incident on the same region of the detector every time the intensity of the electron beam is measured. This means that the sensitivity at which the detector outputs a charge degrades as the detection region of the detector suffers damage upon incidence of an electron beam for a long time.
In the conventional technique, no measure is taken against degradation in sensitivity of the detector due to factors associated with incidence of a charged particle beam on the same region.